personnaly i use lysol for mine and that works pretty well, but some other guys i know have used plenty of other things like bug spray, kerocine (hehehehe), and also several hair care products (ussually the flamable, foreign ones)

Depends on what size your cannon is, and how much you are willing to spend per shot. My main cannon is pneumatic so it is virtually free. but my smaller cannon is run of of bug spray, (its made of a ballpoint pen and a chapstick container). Use this website as a reference http://www.aaroncake.net/spuds/boom.asp, they have a list of pros and cons of each Propellant. http://www.spudfiles.com/ also gives you good information on potato cannons. The three most used propellants are hairspray, propane and deodorants. Propane is expensive and hard to use but burns the best, the other two are good but can gum up your chamber. best of luck to you.